Semiconductor device with buried gates and fabrication method thereof

ABSTRACT

A semiconductor device includes a substrate having a cell region and a peripheral region, a buried gate formed over the substrate of the cell region, a peripheral gate formed over the substrate of the peripheral region and comprising a conductive layer, an inter-layer dielectric layer that covers the substrate, and a peripheral bit line formed inside the inter-layer dielectric layer and contacting the conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No.10-2010-0128055, filed on Dec. 15, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Field

Exemplary embodiments of the present invention relate to a semiconductordevice fabrication technology, and more particularly, to a semiconductordevice including buried gates (BG) and a method for fabricating thesame.

2. Description of the Related Art

As semiconductor devices become smaller in size, a semiconductor devicemay not be able to realize diverse device characteristics. As designrules are less than approximately 40 nm, the formation of a gatestructure, a bit line structure, and a contact structure may havetechnical limitations. Even if such structures are formed, the desireddevice characteristics may not be achieved. To achieve the desireddevice characteristics, semiconductor devices may form buried gates (BG)in a substrate.

FIG. 1 is a cross-sectional view illustrating a conventionalsemiconductor device including buried gates.

Referring to FIG. 1, the conventional semiconductor device with buriedgates includes an isolation layer 12 that defines an active region 13over a substrate 11. The substrate includes a cell region and aperipheral region. In the cell region of the substrate 11, each buriedgate includes a trench 15, a gate insulation layer (not shown), a gateelectrode 16, and a gate hard mask layer 17. Over the substrate 11,landing plugs 14 are formed. An isolation layer 12 is formed to isolatethe landing plugs 14 from another and to isolate the landing plugs 14from the buried gates. In the peripheral region of the substrate 11,peripheral gates 21 are formed, and spacers 22 are formed on thesidewalls of each peripheral gate 21. Each peripheral gate includes aperipheral gate insulation layer 18, a peripheral gate electrode 19, anda peripheral gate hard mask layer 20. An inter-layer dielectric layer 23is formed over the substrate 11, and a storage node contact plug 25 anda cell bit line 28 are formed in the inter-layer dielectric layer 23 ofthe cell region. A portion of a peripheral bit line 31 is coupled withthe peripheral gate electrode 19 and formed in the inter-layerdielectric layer 23 of the peripheral region, while a portion of theperipheral bit line 32 is formed above the inter-layer dielectric layer23. FIG. 1 also illustrates a cell bit line hard mask layer 29, and aperipheral bit line hard mask layer 33.

According to the conventional technology, the peripheral bit line 32 isdisposed over the inter-layer dielectric layer 23 of the peripheralregion. As a result, subsequent processes become complex andprocedurally more difficult. More specifically, step height isinevitably formed between the cell region and the peripheral regionbecause the peripheral bit line 32 is formed over the inter-layerdielectric layer 23. The step height makes the subsequent processes offorming an inter-layer dielectric layer covering the peripheral bit line32 in the peripheral region and forming storage nodes in the cell regionbe complicated, and increases the procedural difficulty. Also, the stepheight between the cell region and the peripheral region cracks an etchstop layer (not shown) interposed between the inter-layer dielectriclayer 23 and a mold-forming insulation layer (not shown) for forming amold, and damages the existing substrate structure during a subsequentdip-out process.

SUMMARY

An embodiment of the present invention is directed to a semiconductordevice with buried gates that may remove the step height occurringbetween a cell region and a peripheral region due to the presence of aperipheral bit line, and a method for fabricating the semiconductordevice.

In accordance with an embodiment of the present invention, asemiconductor device includes: a substrate having a cell region and aperipheral region; a buried gate formed over the substrate of the cellregion; a peripheral gate formed over the substrate of the peripheralregion and including a conductive layer; an inter-layer dielectric layerthat covers the substrate; and a peripheral bit line formed inside theinter-layer dielectric layer and contacting the conductive layer.

In accordance with another embodiment of the present invention, a methodfor fabricating a semiconductor device includes: forming a gateincluding a conductive layer over a substrate; forming an inter-layerdielectric layer that covers the gate; forming a damascene pattern thatexposes the conductive layer by selectively etching the inter-layerdielectric layer and the gate; and forming a bit line that fills thedamascene pattern.

In accordance with yet another embodiment of the present invention, amethod for fabricating a semiconductor device includes: preparing asubstrate having a cell region and a peripheral region; forming a buriedgate over the substrate of the cell region; forming a peripheral gateincluding a conductive layer over the substrate of the peripheralregion; forming a first inter-layer dielectric layer over the substrate;performing a planarization process until the peripheral gate is exposed;forming a second inter-layer dielectric layer over the first inter-layerdielectric layer; forming a peripheral damascene pattern that exposesthe conductive layer by selectively etching the peripheral gate and thesecond inter-layer dielectric layer of the peripheral region; andforming a peripheral bit line that fills the peripheral damascenepattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a conventionalsemiconductor device including buried gates.

FIG. 2 is a cross-sectional view illustrating a semiconductor deviceincluding buried gates in accordance with an embodiment of the presentinvention.

FIGS. 3A to 3E are cross-sectional views illustrating a method forfabricating a semiconductor device including buried gates in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The drawings are not necessarily to scale and in some instances,proportions may have been exaggerated in order to clearly illustratefeatures of the embodiments. When a first layer is referred to as being“on” a second layer or “on” a substrate, it not only refers to a casewhere the first layer is formed directly on the second layer or thesubstrate but also a case where a third layer exists between the firstlayer and the second layer or the substrate.

A semiconductor device including buried gates and not including a stepheight formed between a cell region and a peripheral region, and amethod for fabricating the semiconductor device including the buriedgates is disclosed hereafter. To form the semiconductor device, theperipheral bit line and the cell bit line are formed inside of aninter-layer dielectric layer.

FIG. 2 is a cross-sectional view illustrating a semiconductor deviceincluding buried gates in accordance with an embodiment of the presentinvention.

Referring to FIG. 2, the semiconductor device including buried gatesincludes a substrate 51 having a cell region and a peripheral region,buried gates formed in the cell region of the substrate 51, peripheralgates 62 formed in the peripheral region of the substrate 51, aninter-layer dielectric layer formed over the substrate 51 to cover theperipheral gates 62, storage node contact plugs 67 formed inside of theinter-layer dielectric layer of the cell region, and cell bit lines 70formed inside of the inter-layer dielectric layer of the cell region,and a peripheral bit line 74 formed inside of the inter-layer dielectriclayer of the peripheral region to contact a peripheral gate electrode60. Also, an etch stop layer 75 is formed in the cell region and theperipheral region. The etch stop layer 75 protects the lower structureduring a subsequent process to form storage nodes in the cell region.

An isolation layer 52 that defines an active region 53 is formed in thecell region of the substrate 51. Each buried gate includes a line-typetrench 55, a gate insulation layer (not shown), a gate electrode 56, anda gate hard mask layer 57. The line-type trench 55 crosses an activeregion 53 and the isolation layer 52. The gate insulation layer fills aportion of the trench 55. The gate hard mask layer 57 fills theremaining portion of the trench 55. Landing plugs 54, which are definedby the isolation layer 52, and the buried gates are formed in the cellregion of the substrate 51.

The isolation layer 52 that defines the active region 53 is formed inthe peripheral region of the substrate 51. In the peripheral region ofthe substrate 51, peripheral gates 62 are formed. Each peripheral gate62 has a stacked structure. To form the stack structure, a peripheralgate insulation layer 59, a peripheral gate electrode 60, and aperipheral gate hard mask layer 61 are sequentially stacked. Theperipheral gate electrode 60 may be formed of a conductive layer.

An inter-layer dielectric layer is formed over the substrate 51 in boththe cell region and the peripheral region. The inter-layer dielectriclayer has a stacked structure formed by sequentially stacking a firstinter-layer dielectric layer 64 and a second inter-layer dielectriclayer 65. The first inter-layer dielectric layer 64 has its uppersurface disposed on the same plane as the upper surfaces of theperipheral gates 62, and the second inter-layer dielectric layer 65 isformed over the first inter-layer dielectric layer 64. The firstinter-layer dielectric layer 64 and the second inter-layer dielectriclayer 65 may be formed of the same material, and the second inter-layerdielectric layer 65 may have a higher dielectric constant than the firstinter-layer dielectric layer 64.

Storage node contact plugs 67 and cell bit lines 70 that penetrate thefirst inter-layer dielectric layer 64 and the second inter-layerdielectric layer 65 are formed inside of the first inter-layerdielectric layer 64 and the second inter-layer dielectric layer 65. Thecell bit line 70 fills a portion of a cell damascene pattern 68 that hasa line shape stretched in a direction crossing the buried gates. Bitline spacers 69 are formed on the sidewalls of the cell damascenepattern 68, and a bit line hard mask layer 71 is formed by filling theremaining portion of the cell damascene pattern 68.

A peripheral bit line 74 is formed inside of the inter-layer dielectriclayer of the peripheral region, and fills a peripheral damascene pattern73. The peripheral damascene pattern 73 includes a hole pattern 73A thatexposes the peripheral gate electrode 60 and a line pattern 73B that iscoupled with the hole pattern 73A.

Since the above-described semiconductor device has a structure where theperipheral bit line 74 is buried inside of the inter-layer dielectriclayer, the formation of a step height between the cell region and theperipheral region may be prevented. Therefore, procedural difficulty ofa subsequent process for forming storage nodes in the cell region may bereduced, and the etch stop layer 75 may be protected from cracking thatis caused due to the presence of the step height.

FIGS. 3A to 3E are cross-sectional views illustrating a method forfabricating a semiconductor device including buried gates in accordancewith an embodiment of the present invention.

Referring to FIG. 3A, a hard mask pattern (not shown) is formed over asubstrate 51 having a cell region and a peripheral region, and anisolation layer 52 defining an active region 53 is formed by using thehard mask pattern. The isolation layer 52 may be formed through aShallow Trench Isolation (STI) process.

Subsequently, the hard mask pattern of the cell region is removed, and alanding plug-forming conductive layer (not shown) fills a groove that isformed as a result of the removal of the hard mask pattern of the cellregion.

Subsequently, landing plugs 54 are formed over the substrate 51 of thecell region, and a plurality of buried gates are formed over thesubstrate 51. The buried gates may be formed by first selectivelyetching the landing plug-forming conductive layer (not shown), theactive region 53, and the isolation layer 52 to form trenches 55. Afterthe forming the trenches 55, the buried gates maybe formed by forming agate insulation layer (not shown) on the surfaces of the trenches 55,forming a gate electrode 56 filling a portion of each trench 55, andforming a gate hard mask layer 57 filling the other portion of eachtrench 55 over the gate electrode 56. The landing plugs 54 are formedwhen the trenches 55 for forming buried gates are formed.

Subsequently, a first capping layer 58 that covers the cell region isformed over the substrate 51, and the substrate 51 of the peripheralregion is exposed using the first capping layer 58. In the course ofexposing the substrate 51 of the peripheral region, a portion of theisolation layer 52 may be lost. If a portion of the isolation layer 52is lost, the surface of the active region 53 and the surface of theisolation layer 52 may be on the same plane in order to facilitate thesubsequent process by performing additional processes on the activeregion 53 and the isolation layer 52.

Referring to FIG. 3B, peripheral gates 62 are formed by sequentiallystacking a peripheral gate insulation layer 59, a peripheral gateelectrode 60, and a peripheral gate hard mask layer 61 over thesubstrate 51 of the peripheral region. The height of the peripheral gatehard mask layer 61 is controlled to be as low as possible so that thetotal height of the peripheral gates 62 may be as low as possible. Theheight of the peripheral gates 52 is set as low as possible to improvethe gap-fill characteristics in the subsequent process that forms aninter-layer dielectric layer and to improve the stability of the processthat forms the peripheral gates 62 by decreasing the aspect ratio of theperipheral gates 62. Moreover, when the peripheral gates 62 are formedto have a low height, the space where a peripheral bit line is to beformed may be stably provided.

Subsequently, spacers 63 are formed on the sidewalls of each peripheralgate 62, and the first capping layer 58 covering the cell region isremoved.

Referring to FIG. 3C, a first inter-layer dielectric layer 64 is formedto cover the entire surface of the substrate 51, and subsequently aplanarization process is performed until the peripheral gates 62 areexposed. The planarization process may be a Chemical MechanicalPolishing (CMP) process.

Since the height of the peripheral gates 62 is made to be low, the firstinter-layer dielectric layer 64 is easily gap-filled and many differentmaterials may be used to form the first inter-layer dielectric layer 64.Therefore, a material having a better film quality but poorer gap-fillcharacteristics than the materials used in the conventional technologymay be used to form the first inter-layer dielectric layer 64. Since theperipheral gates 62 have a high aspect ratio in the semiconductor deviceof the conventional technology, a material used in the conventionaltechnology has excellent gap-fill characteristics, although a poor filmquality, such as a Spin-On-Dielectric (SOD).

Subsequently, a second inter-layer dielectric layer 65 is formed overthe first inter-layer dielectric layer 64. The second inter-layerdielectric layer 65 is formed to have a thickness to sufficientlyprovide a space where a cell bit line and storage node contact plugs ofthe cell region are to be formed and a space where a peripheral bit lineof the peripheral region is to be formed. The second inter-layerdielectric layer 65 may be formed of the same material as the firstinter-layer dielectric layer 64 to facilitate the subsequent process.

The second inter-layer dielectric layer 65 may be formed of a materialhaving a lower porosity and a higher hardness than the first inter-layerdielectric layer 64. Also, the second inter-layer dielectric layer 65may be formed of a material having a higher stability to an etchsolution or a cleaning solution than the first inter-layer dielectriclayer 64. As a result, the stability of the subsequent processes forforming storage node contact plugs and cell bit lines may be increased,and a short may be prevented from occurring between the storage nodecontact plugs and the cell bit line.

Subsequently, storage node contact holes 66 that expose the landingplugs 54 are formed by selectively etching the second inter-layerdielectric layer 65 and the first inter-layer dielectric layer 64. Thestorage node contact holes 66 may be formed in one shape selected fromthe group consisting of a hole type, a bar type, and a line type. Thehole type shape individually exposes the landing plugs 54 of a regionreserved for the storage node contact plugs. The bar type shapesimultaneously exposes the landing plugs 54 of an adjacent regionreserved for the storage node contact plugs. A line type shapesimultaneously exposes the landing plugs 54 of a region reserved for thestorage node contact plugs, which are disposed on the same line.

Subsequently, storage node contact plugs 67 are formed by filling thestorage node contact holes 66 with a conductive material. The storagenode contact plugs 67 may be formed through a series of processes ofdepositing a conductive layer to fill the storage node contact holes 66and performing a planarization process until the second inter-layerdielectric layer 65 is exposed. Since the second inter-layer dielectriclayer 65 is formed over the peripheral gate hard mask layer 61, theplanarization process for isolating adjacent storage node contact plugs67 may be performed easily.

Referring to FIG. 3D, a cell damascene pattern 68 is formed byselectively etching the second inter-layer dielectric layer 65 and thefirst inter-layer dielectric layer 64 of the cell region. The celldamascene pattern 68 is formed to expose the landing plugs 54 disposedin the central portion of the active region 53. The cell damascenepattern 68 has a line shape stretched in a direction crossing the buriedgates.

When the storage node contact holes 66 are formed in a bar type or aline type, the conductive layer filling the storage node contact holes66 is etched along with the first inter-layer dielectric layer 64 andthe second inter-layer dielectric layer 65 during the process of formingthe cell damascene pattern 68, and through the etching process, thestorage node contact plugs 67 are formed.

Subsequently, bit line spacers 69 are formed on the sidewalls of thecell damascene pattern 68. The bit line spacers 69 may be formed as asingle layer selected from the group consisting of an oxide layer, anitride layer, and an oxynitride layer, or a stacked layer thereof.

Subsequently, a cell bit line 70 that fills a portion of the celldamascene pattern 68 is formed, and a bit line hard mask layer 71 thatfills the other portion of the cell damascene pattern 68 is formed overthe cell bit lines 70.

Subsequently, a second capping layer 72 is formed over the substrate 51.The second capping layer 72 protects the structures that are alreadyformed in the cell region from being damaged during a subsequent processthat forms a peripheral bit line.

Referring to FIG. 3E, a hole pattern 73A that exposes the peripheralgate electrode 60 is formed by selectively etching the second cappinglayer 72, the second inter-layer dielectric layer 65, and the peripheralgate hard mask layer 61 of the peripheral region. Subsequently, a linepattern 73B coupled with the hole pattern 73A is formed by selectivelyetching the second capping layer 72 and the second inter-layerdielectric layer 65 of the peripheral region. As a result, a peripheraldamascene pattern 73 including the hole pattern 73A and the line pattern73B may be formed. The peripheral damascene pattern 73 provides a spacewhere a peripheral bit line is to be formed.

Subsequently, a peripheral bit line 74 coupled with the peripheral gateelectrode 60 is formed by forming spacers (not shown) on the sidewallsof the peripheral damascene pattern 73, and then depositing a conductivelayer to fill the peripheral damascene pattern 73, and performing aplanarization process until the second inter-layer dielectric layer 65is exposed.

Subsequently, an etch stop layer 75 is formed over the substrate 51.Although not illustrated in the drawing, an insulation layer for a moldmay also be formed over the etch stop layer 75, and a process forforming storage nodes and a wet dip-out process are sequentiallyperformed.

According to an embodiment of the present invention, the formation ofstep height between a cell region and a peripheral region may beprevented by forming a peripheral bit line inside of an inter-layerdielectric layer. Therefore, procedural difficulty of a subsequentprocess for forming storage nodes in the cell region may be reduced, andthe etch stop layer 75 may be protected from cracking caused by thepresence of the step height.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A semiconductor device, comprising: a substrate having a cell regionand a peripheral region; a buried gate formed over the substrate of thecell region; a peripheral gate formed over the substrate of theperipheral region and comprising a conductive layer; an inter-layerdielectric layer that covers the substrate; and a peripheral bit lineformed inside the inter-layer dielectric layer and contacting theconductive layer.
 2. The semiconductor device of claim 1, furthercomprising: a storage node contact plug penetrating the inter-layerdielectric layer of the cell region; a cell damascene patternpenetrating the inter-layer dielectric layer of the cell region; bitline spacers formed on sidewalls of the cell damascene pattern; a cellbit line filling a portion of the cell damascene pattern; and a bit linehard mask layer filling the other portion of the cell damascene pattern.3. The semiconductor device of claim 1, wherein the peripheral bit linefills a peripheral damascene pattern structure that includes a holepattern that is formed in the inter-layer dielectric layer and exposesthe conductive layer and a line pattern coupled with the hole pattern.4. The semiconductor device of claim 1, wherein the inter-layerdielectric layer comprises: a first inter-layer dielectric layer whoseupper surface is disposed on the same plane as an upper surface of theperipheral gate, formed in the cell region and the peripheral region;and a second inter-layer dielectric layer formed over the firstinter-layer dielectric layer and having a higher dielectric constantthan the first inter-layer dielectric layer.
 5. The semiconductor deviceof claim 4, wherein the first inter-layer dielectric layer and thesecond inter-layer dielectric layer are formed of the same materials.6-17. (canceled)
 18. The semiconductor device of claim 1, wherein theperipheral gate is formed at a different level from the buried gate. 19.The semiconductor device of claim 1, further comprising: a storage nodecontact plug penetrating the inter-layer dielectric layer of the cellregion, wherein the peripheral bit line is formed at the same level asthe storage node contact plug in the cell region.